1. Field of the Invention
The present invention relates to a method of and apparatus for inspecting a circuit board, such as a flip-chip bonding circuit board and a ball grid array (BGA) circuit board, on which is arranged two-dimensionally a plurality of solder balls or bumps for electrical connection with a chip or another circuit board (circuit board with solder bumps being herein refered to as "bump-attached circuit board"). The present invention further relates to a method of producing a bump-attached circuit board by the use of such an inspection method and apparatus.
2. Description of the Related Art
In recent years, there is an increasing tendency that integrated circuit chips, such as microprocessor chip and computer chips are becoming higher in the density of integration and rapidly increasing in the number of input/output terminals. For connecting such a chip to a circuit board substrate by the flip-chip technology, solder bumps formed on the substrate are several hundreds at least and several thousands at most in number. In this connection, if the solder bumps formed on the substrate are, for example, not in place or the height and other dimensions thereof are not included within predetermined ranges, there arises a problem that a defective connection is caused between the circuit board and a mating chip and a malfunction of an integrated circuit chip may possibly be caused, so strict inspection of the solder bumps is needed.
Heretofore known as the most popular inspecting technique for inspecting the dimensions of the solder bumps of such a bump-attached circuit board, for example, the heights of the solder bumps is a measurement technique using a laser beam. However, by this measurement technology, it takes several seconds to measure the height of one solder bump. Thus, in case of the substrate having a great number of solder bumps, it takes a time ranging from several tens of minutes to several hours to measure the heights of all the solder bumps on one circuit board, so it is actually impossible to carry out 100% inspection of mass-produced circuit boards.
To solve such a problem, there is proposed, as disclosed in JP 6-167322, an apparatus for carrying out high-speed inspection of the heights of solder bumps by scanning a main surface of a circuit board in its entirety with a spot light, inputting a data on the heights of all the surface sections of the circuit board including the surface sections provided with the solder bumps, and determining a height of a solder bump on the basis of the difference between the height of the top of the solder bump and the height of the main surface of the circuit board.
The object to be inspected by such an apparatus disclosed in the above described Japanese patent provisional publication is a semiconductor silicon circuit board having spherical solder bumps, and the apparatus is adapted to measure the heights of the solder bumps by the use of the reflected beam reflected from the place around the top of each solder bump, which is masked by the data on brightness. However, in the case this technique is used for measuring the height of a solder bump having a flat or flattened top (hereinafter referred to as flat solder bump), there occurs the following problem. That is, in the case the outer surface of the solder bump is spherical, there is caused, in measurement of the brightness of beam reflected from the solder bump, a region which is high in the reflection brightness (hereinafter referred to as high brightness region) and which is located limitedly adjacent the top of the solder bump, so that it can be easily judged which of high brightness regions corresponds to which of the solder bumps. Further, when viewing this matter from another angle, in the circuit board having a plurality of spherical solder bumps, there is caused at a point adjacent the top of each solder bump only one data on height corresponding to each solder bump. Thus, there will not be caused any confusion about judgment on which of two or more of data on height being derived from which of the solder bumps.
However, in the case of the flat solder bump, the high brightness region derived from one solder bump has a certain extent since the top of the solder bump is flat, so a number of height data corresponding to various places on the top are prepared even when the top of only one solder bump is scanned with a laser beam. That is, a number of height data are obtained for only one solder bump. As a result, a relation of one to one correspondence does no more exist between a height data and a solder bump, for example, it will become unclear whether two height data which are relatively close in position to each other are derived from the same solder bump or different solder bumps, resulting in a drawback that it becomes impossible to determine the heights of the solder bumps accurately.
In this instance, two height data derived from different solder bumps belong to two high brightness regions which are separated by a low brightness region, so it appears seemingly possible to determine whether two high brightness regions belong to different solder bumps or to the same solder bump. However, in the case of the solder bump having a depression on the top, a low brightness region corresponding to the depression is produced within a reflected image of one solder bump, so that two height data with a low brightness region therebetween can not be readily judged as being derived from two different solder bumps.
Further, in the apparatus disclosed by the above described Japanese patent provisional publication, for inspecting a surface luster, a line sensor is used for picking up image of bumps on a circuit board surface. In this instance, the information represented by the picked-up image reflects the intensity of the reflected beam at respective positions on the circuit board and does not include information on height. For this reason, while a pair of bumps which are different in the surface condition due to oxidation or the like can be distinguished from each other, it is impossible to distinguish a bump of a normal height from a bump of an abnormal height on the basis of a picked-up image unless there is a difference in the surface condition between them. In the above described prior art apparatus, in addition to the information based on the picked-up image, reference is also made to the information on the bump height measured by PSD (position sensing device). However, it is impossible to grasp intuitively whether the height of each bump formed on the circuit board is good or not, and there arises a problem that even an obvious height defect cannot be found unless reference is made to the height information which is measured separately.
Further, in case a variation in the height level of the surface of the circuit board is caused due to warping, waviness or the like, the absolute height level of the top position of each bump is not uniform even if the protruding height of each bump is uniform, thus possibly causing a connection defect or the like. However, since evaluation of the bump height is performed on the basis of only the protruding height above the circuit board surface by the above described prior art apparatus, there results a problem that such a height level defect of the height level being not uniform (i.e., a so-called coplanarity defect) cannot be found. Further, since the above described picked-up image does not almost reflect any information on the bump top position, height level distribution, warping or waviness of the circuit board surface, etc., it is almost hopeless to find the above described defects on the basis of the picked-up image.